The present invention relates to a cup for a master cylinder, a master cylinder, advantageously a tandem master cylinder, fitted with such cups, coming into contact with its primary piston or its secondary piston and said elements being subjected to the pressure of the brake fluid of the primary chamber and of the secondary chamber.
The cup in the shape of a seal with a section like a U on its side being housed in a groove of the bore of the body of the master cylinder receiving the primary and secondary pistons, the outer lip of the cup being pressed against the bottom of the groove and its inner lip being pressed by its outer surface against the piston (primary or secondary), this outer surface of revolution having, between the end of the lip and the bottom of the cup, a section forming a heel followed by a corrugated profile comprising at least two large grooves and a succession of small grooves forming with the piston annular cavities trapping the brake fluid.
There are such isolating/separating tandem master-cylinder cups subjected to the pressure of the brake fluid of the primary chamber and of the secondary chamber described in document EP 1616768 A1, which have a lip or a heel being pressed over the whole peripheral surface against the peripheral surface of the primary piston or of the secondary piston of the master cylinder. This heel or lip is followed by grooves, namely first two large grooves then a succession of small grooves forming peripheral volumes receiving fluid and the partitions between the grooves being pressed, when the tandem master cylinder is under pressure, against the surface of the primary and secondary pistons.